The valve adjustment of multi-cylinder engines is generally adjusted in two adjustments. The method is: for a general 4-cylinder engine, the ignition sequence is 1-3-4-2, first align the top dead center mark of cylinder 1, and then adjust the intake and discharge of cylinder 1. , 2 cylinders in, 3 rows. Align the top dead center mark of cylinder 4 with one rotation of the crankshaft, and then adjust cylinder 4 to enter row, 3 cylinder to enter, and 2 row. The mouth decision is 1.2.3.6 advanced back row.
What’s more, the valve speed argument can not be restricted by adjusting the valve clearance to be in-line 1-4 or 1-6 top dead center, as long as you know that any cylinder piston is at compression top dead center, you can adjust half of the valve. “Upper cylinder” enters the “lower cylinder” row. “This cylinder” double this cylinder: refers to the cylinder whose piston is at the top dead center of the compression stroke. Upper cylinder: refers to the cylinder whose ignition sequence is before this cylinder.
In: is the intake valve
Lower cylinder: the cylinder behind this cylinder
Row; it’s just a row.
Example 1: The ignition sequence of inline 4 cylinders is 1-3-4-2
When 3 is at compression top dead center, it is recognized that the adjustable valve is. 1-cylinder intake valve, 4-cylinder exhaust valve and 3-cylinder intake and exhaust valve.
Example 2: The ignition sequence of inline 6 cylinders is 1-5-3-6-2-4
When 3 is at compression top dead center, it is recognized that the adjustable valve is. 3-cylinder intake and exhaust valves. 1,5-cylinder intake valve, 6,2-cylinder exhaust valve
1. The meaning of valve clearance
The heads of the intake and exhaust valves are directly located in the combustion chamber, and the entire head of the exhaust valve is located in the exhaust passage, so the temperature is very high. At such a high temperature, the valve will expand due to thermal expansion. Since the valve train parts are rigid bodies, if there is no valve gap between the parts in the cold state, the heated and expanded valve will cause the valve to close loosely and leak air, resulting in a decrease in engine power, an increase in fuel consumption, and an increase in engine power. It cannot even start due to overheating. Therefore, when the engine is assembled in a cold state, there must be a certain valve clearance between the valve group and the valve drive group. During the operation of the engine, the size of the valve clearance will change, so a valve clearance adjustment device is provided in the valve mechanism to adjust the valve clearance.
2. Adjust the valve clearance by “twice adjustment method”
The so-called “twice adjustment method” means that all the valves of a multi-cylinder engine can be checked and adjusted as long as the crankshaft of the engine is rotated twice.
“Twice adjustment method”-“Double row no entry method”
The “double” of the “double-row no-entry method” means that the clearance between the two valves of the cylinder at the top dead center can be adjusted, the “row” means that the clearance of the exhaust valve of the cylinder can be adjusted, and the “no” means that the two valve clearances of the cylinder can be adjusted. The valve clearance is not adjustable, “in” means that the cylinder’s intake valve clearance can be adjusted.
“Two adjustment method” operating procedures
Rotate the crankshaft and find the top dead center of the compression stroke of the first cylinder according to the timing mark;
(1) According to the working sequence of the engine, determine the adjustable valve according to the principle of “double, row, no, and enter”, and then check and adjust the valve clearance;
(2) Rotate the crankshaft one more circle to align the timing mark, and use the same method to check and adjust the remaining valve clearances. So far, all valve inspections and adjustments have been completed.
3. Issues that should be paid attention to when adjusting the valve clearance with the “twice adjustment method”
For engines of different structures, the arrangement of the intake and exhaust valves may not be the same, and the valve should be clearly identified before adjusting the valve.
It cannot be mistaken whether a cylinder is at compression top dead center or exhaust top dead center.
Generally, there are timing marks on the engine. When the timing mark is aligned, it may be that one cylinder is at compression top dead center, or it may be that one cylinder is at exhaust top dead center. At this time, when the crankshaft is rotated by an angle counterclockwise, the exhaust valve of one cylinder has an opening movement; when the crankshaft is rotated an angle clockwise, the intake valve of one cylinder has an opening movement, and the other cylinder is at the exhaust top dead center. If the two valves of a cylinder do not open, it means that the cylinder is at compression top dead center.
For engines with the same number of cylinders, if the working sequence is different, the valve adjustment sequence is also different.
Different types of engines have different valve clearances; the same type of engine has different valve clearances in cold and hot states; the same type of engine has different intake and exhaust valve clearances. The adjustment must be made according to the standard according to the maintenance manual.
After all the valves are adjusted, they must be checked again to ensure that the clearance of each valve fully meets the standard requirements.
For engines with hydraulic tappets, since the tappet length can be changed automatically, there is no need to reserve valve clearance, so there is no valve clearance adjustment device, so there is no need to adjust the valve clearance.
I am also a maintenance person, this line is very hard, I have also sorted out a bit myself, I hope it will be helpful to you:
The first is the cylinder-by-cylinder adjustment method. This is a textbook adjustment method. It is simple and basically suitable for novices to understand and master. It is more cumbersome when adjusting a multi-cylinder engine; therefore, ordinary maintenance personnel do not use this method.
The second is the two-time adjustment method, which is the most widely used valve adjustment method, and it is also a method that most people agree with. Some experienced maintenance engineers can directly find the valve to be adjusted based on their experience. For those who are new to contact, the method of “double-row no entry” is recommended to adjust the valve. The “double row no entry” method is a universal and simple valve clearance adjustment method. It divides the adjustment of the valves of each cylinder into four types according to the order of the engine’s work: “Double” means that the cylinder enters and exhausts. The doors are adjustable;
“Exhaust” means that only the exhaust valve of the cylinder can be adjusted;
“No” means that the cylinder’s intake and exhaust valves are not adjustable;
“In” means that the cylinder can only adjust the intake valve.
The last thing to note is:
1. For engines of different structures, the arrangement of the intake and exhaust valves may not be the same, and the valve should be clearly identified before adjusting the valve.
2. It cannot be mistaken whether a cylinder is at compression top dead center or exhaust top dead center.
Generally, there are timing marks on the engine. When the timing mark is aligned, it may be that one cylinder is at compression top dead center, or it may be that one cylinder is at exhaust top dead center. At this time, when the crankshaft is rotated by an angle counterclockwise, the exhaust valve of one cylinder has an opening movement; when the crankshaft is rotated an angle clockwise, the intake valve of one cylinder has an opening movement, and the other cylinder is at the exhaust top dead center. If the two valves of a cylinder do not open, it means that the cylinder is at compression top dead center.
3. For engines with the same number of cylinders, if the working sequence is different, the valve adjustment sequence is also different.
4. Different types of engines have different valve clearances; the same type of engine has different valve clearances in cold and hot states; the same type of engine has different intake and exhaust valve clearances. When adjusting, it must be adjusted according to the standard according to the maintenance manual
